SIEMENS
6/20
Siemens IC 10 · 2017
SIRIUS 3RW Soft Starters
3RW30, 3RW40 for Standard Applications
3RW40
General data
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Overview
SIRIUS 3RW40 soft starters
SIRIUS
3RW40
soft starters have all the same advantages as the
3RW30 soft starters.
The SIRIUS 3RW40 soft starters are characterized above all by
their small space requirements. Integrated bypass contacts
mean that no power loss has to be taken into the bargain at the
power semiconductors (thyristors) after the motor has started
up. This cuts down on heat losses, enabling a more compact
design and making external bypass circuits superfluous.
At the same time this soft starter comes with additional
integrated functions such as adjustable current limiting, motor
overload and intrinsic device protection, and optional thermistor
motor protection. The higher the motor rating, the more
important these functions, because they make it unnecessary to
purchase and install protection equipment such as overload
relays.
Internal intrinsic device protection prevents the thermal
overloading of the thyristors and the power section defects this
can cause. As an option the thyristors can also be protected by
semiconductor fuses from short-circuiting.
Thanks to integrated status monitoring and fault monitoring, this
compact soft starter offers many different diagnostics options.
Up to four LEDs and relay outputs permit differentiated
monitoring and diagnostics of the operating mechanism by
indicating the operating state as well as for example mains or
phase failure, missing load, non-permissible tripping
time/CLASS setting, thermal overloading or device faults.
Soft starters rated up to 250 kW (at 400 V) for standard
applications in three-phase networks are available. Extremely
small sizes, low power losses and simple start up are just three
of the many advantages of the SIRIUS 3RW40 soft starters.
"Increased safety" type of protection EEx e according to
ATEX directive 94/9/EC
The 3RW40 soft starter sizes S0 to S12 are suitable for the
starting of explosion-proof motors with "increased safety" type of
protection EEx e.
Functionality
The space required by the compact SIRIUS 3RW40 soft starter
is often only about one third of that required by a contactor
assembly for wye-delta starting of comparable rating. This not
only saves space in the control cabinet and on the standard
mounting rail but also does away completely with the wiring work
needed for wye-delta starters.
This is notable in particular for higher motor ratings which are
only rarely available as fully wired solutions.
At the same time the number of cables from the starter to the
motor is reduced from six to three. Compact dimensions, short
start-up times, easy wiring and fast commissioning make
themselves felt as clear-cut cost advantages.
The bypass contacts
of these soft starters are protected during
operation by an integrated solid-state arc quenching system.
This prevents damage to the bypass contacts in the event of a
fault, e.g. brief disconnection of the control voltage, mechanical
shocks or life-related component defects on the coil operating
mechanism or main contact spring.
The starting current of particularly powerful operating
mechanisms can place an unjustifiable load on the local supply
system. Soft starters reduce this starting current by means of
their voltage ramp. Thanks to the adjustable current limiting
, the
SIRIUS 3RW40 soft starter takes even more pressure off the
supply system. It leaves the set start ramp during the ramp-up –
the ramp gradient is fixed by the starting voltage and the ramp
time – as soon as the selected current limit is reached.
From this moment the voltage of the soft starter is controlled so
that the current supplied to the motor remains constant. This
process is ended either by completion of the motor ramp-up or
by tripping by the intrinsic device protection or the motor
overload protection. As the result of this function the actual motor
ramp-up can well take longer than the ramp time selected on the
soft starter.
Thanks to the integrated motor overload protection
according to
IEC 60947-4-2, there is no need for an additional overload relay
on the new soft starters. The rated motor current, the setting of
the overload tripping time (CLASS times) and the reset of the
motor overload protection function can be adjusted easily and
quickly. Using a 4-step rotary potentiometer it is possible to set
different overload tripping times on the soft starter. In addition to
CLASS 10, 15 and 20 it is also possible to switch off the motor
overload protection if a different motor management control
device is to be used for this function, e.g. with connection to
PROFIBUS.
Device versions with thermistor motor protection evaluation
are
available up to a rating of 55 kW (at 400 V). A "Thermoclick"
measuring probe can be connected directly, as can a PTC of
type A. Thermal overloading of the motor, open circuits and
short circuits in the sensor circuit all result in the direct
disconnection of the soft starter. And if ever the soft starter trips,
various reset options are available the same as with intrinsic
device protection and motor load protection: manually with the
reset button, automatically or remotely through brief
disconnection of the control voltage.
The series of devices comes with the "polarity balancing" control
method
, which is designed to prevent direct current components
in two-phase controlled soft starters. On two-phase controlled
soft starters the current resulting from superimposition of the two
controlled phases flows in the uncontrolled phase. This results
for physical reasons in an asymmetric distribution of the three
phase currents during the motor ramp-up. This phenomenon
cannot be influenced, but in most applications it is non-critical.
Controlling the power semiconductors results not only in this
asymmetry, however, but also in the previously mentioned direct
current components which can cause severe noise generation
on the motor at starting voltages of less than 50 %.
The control method used for these soft starters eliminates these
direct current components during the ramp-up phase and
prevents the braking torque which they can cause. It creates a
motor ramp-up that is uniform in speed, torque and current rise,
thus permitting a particularly gentle, two-phase starting of the
motors. At the same time the acoustic quality of the starting
operation comes close to the quality of a three-phase controlled
soft starter. This is made possible by the on-going dynamic
harmonizing and balancing of current half-waves of different
polarity during the motor ramp-up. Hence the name "polarity
balancing".
© Siemens AG 2016